I have always had leos born with a small yolk sac- about the size of a pencil lead. I have had leos have a gestation of at least 122 days but no more than 129 days (pregnancy confirmed by ultrasound- not determined by mating behavior). Gestation time seems to vary a bit in my experience. Keep in mind that some elasmos can delay implantation of fertile ova, so it may not always possible to determine start date of gestation based on chew marks/mating behavior. If you are still seeing movement (indicating pups are still alive) and she is still eating I wouldn't worry too much about it. Had a ray hold on to a dead pup for several days before expelling it and she did fine. As long as mom is still eating she is probably alright.